I was curious to try an IDE on Osx for Rails development and APTANA STUDIO seems to be the right product. (I do use TextMate as editor)

Aptana Studio is fully installed on my laptop but, when I try to install the RedRails plugin, it returns this error:

Requested operation cannot be performed because it would invalidate the current configuration. See details for more information.

Ruby Mylyn Connector Feature (Optional) (0.9.3.6479) requires feature
"org.eclipse.mylyn.context_feature (2.0.0.v20070628-1000)", or later version.

The solution: http://support.aptana.com/issues/browse/ROR-156

The most important steps are:

1. Went to Help=>Updates=>Find and Install. Installed three Eclipse updates that the system found. Installation of updates worked ok.
2. When the update window appears with RadRails updates, expand the tree and uncheck the box next to the Ruby Mylyn Connector Feature. This is an optional extension for users of Mylyn. You don’t need it, so you can safely uncheck the box and install.

This seems to works either on Windows, Osx and Linux

It might be a problem, an “old” well-known issue…

sudo gem install mysql

might return an error like:

ERROR:  While executing gem ... (Gem::Installer::ExtensionBuildError)

    ERROR: Failed to build gem native extension.

Well, this is cause you need the -dev environment of mysql. Too easy to think that it could be mysql-dev, no! just try

apt-get install libmysqlclient15-dev

It will works!